DIM Supplements and Estrogen: Trials Show Shifts in Lab Markers, Not Proven Symptom Relief
DIM (diindolylmethane) is sold online for "estrogen balance", hormonal acne and PMS. In trials it changed how estrogen is broken down and raised a hormone-binding protein, but those are lab markers, the larger trials found no effect on the outcomes they targeted, and it lowered active tamoxifen levels. Here is what each trial found, who paid for it, and who should be careful.
By Kymata Health Editorial Published Last checked
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Key takeaways
From 5 sources- In a 12-month trial of 130 women taking tamoxifen, DIM 150 mg twice daily raised the urinary 2/16α-hydroxyestrone ratio and the hormone-binding protein SHBG, but breast density did not change1.
- The same trial found lower blood levels of tamoxifen's active forms, including endoxifen, on DIM; whether that weakens tamoxifen is unknown1.
- The largest trial, 551 women with mildly abnormal smear tests, found no clear effect of DIM 150 mg a day on cervical changes or HPV after 6 months2.
- None of the trials described here tested hormonal acne, PMS, weight loss or "estrogen dominance" symptoms, which are common reasons DIM is marketed.
- Darker urine is the most common side effect: 31% on DIM versus 10% on placebo in the largest trial2.
What this article covers
1 evidence profileThe evidence, graded
Pulled from the trial tables in our evidence profiles. Grades follow our evidence-grading policy.
Graded findings
4 rows- CGrade CEstrogen metabolism, breast density and tamoxifen metabolites in women taking tamoxifenMixed The urinary 2/16α-hydroxyestrone ratio and SHBG rose versus placebo. Breast density on mammography and MRI did not change. Plasma endoxifen, 4-hydroxytamoxifen and N-desmethyltamoxifen fell versus placebo (P<0.001), and more women dropped below a proposed endoxifen threshold of 5.6 ng/mL.DIM (diindolylmethane) · RCT · n=130 · 2017 · PMID 28560655
- CGrade CCervical cytology, CIN2+ and HPV in low-grade cervical abnormalitiesNo effect CIN2 or worse in 9% on DIM vs 12% on placebo (RR 0.7, 95% CI 0.4–1.2); CIN3 or worse RR 0.9 (0.4–2.0). HPV persisted in 69% on DIM vs 61% on placebo (RR 1.1). The authors concluded DIM is unlikely to affect cytology or HPV, with uncertainty about CIN2+.DIM (diindolylmethane) · RCT · n=551 · 2012 · PMID 22075942
- DGrade DCervical lesions (CIN2–3) before planned excisionNo effect No statistically significant difference between DIM and placebo in any outcome; 2 people on DIM reported nausea.DIM (diindolylmethane) · Pilot RCT · n=64 · 2010 · PMID 19939441
- DGrade DProstate tissue DIM and biomarkers before prostatectomyMixed DIM was found in only 7 of 28 prostate tissue samples. The urinary 2/16-hydroxyestrone ratio changed versus placebo in the 400 mg/day group; PSA, testosterone and other markers did not change significantly.DIM (diindolylmethane) · RCT · n=45 · 2016 · PMID 26313229
What DIM is and what the estrogen claim means
DIM, short for 3,3'-diindolylmethane, forms in the body from indole-3-carbinol, a compound in cruciferous vegetables, and it is also sold as a supplement15.
The "estrogen balance" claim rests on lab markers. The urinary 2/16 ratio compares two estrogen breakdown products, 2-hydroxyestrone and 16α-hydroxyestrone, and in a 12-month trial DIM raised that ratio and raised sex hormone-binding globulin (SHBG), a blood protein that binds sex hormones1. A change in these markers is not the same as relief from any symptom.
The tamoxifen trial: markers moved, density did not
In a randomized trial, 130 women prescribed tamoxifen after breast cancer were randomized to a formulated DIM product (BioResponse DIM) at 150 mg twice daily or placebo for 12 months; 98 completed1.
The urinary 2/16α-hydroxyestrone ratio rose by 3.2 on DIM versus a fall of 0.7 on placebo, and SHBG rose by an average of 25 nmol/L versus 1.1 nmol/L1. Breast density on mammograms and MRI did not change1.
Blood levels of tamoxifen's active breakdown products endoxifen and 4-hydroxytamoxifen, and of N-desmethyltamoxifen, were lower on DIM than placebo (P < 0.001)1. The authors said more research is needed to know whether this blunts tamoxifen's benefit1.
The trial was funded by US National Cancer Institute grants, and the authors reported no conflicts of interest1.
The larger trials found no clear effect
A UK trial randomized women with newly found low-grade abnormal smear tests 2:1 to 150 mg of DIM (from BioResponse DIM) or placebo daily for 6 months, and analysed 551 of them2. Moderate or worse cervical changes (CIN2+) were found in 9% on DIM and 12% on placebo, a difference that could be chance (risk ratio 0.7, 95% CI 0.4 to 1.2)2. Among women with HPV at the start, 69% on DIM and 61% on placebo still had it at 6 months2. The trial was funded by Cancer Research UK2.
A pilot trial gave 64 women with CIN2 or CIN3 about 2 mg/kg of DIM a day or placebo for 12 weeks, with both capsules supplied by BioResponse; many women in both groups improved, and there was no statistically significant difference between them3.
In 45 men awaiting prostate surgery, 100 or 200 mg of DIM twice daily for 3 to 4 weeks reached measurable levels in only 7 of 28 prostate tissue samples, and PSA and testosterone did not change significantly4. That trial was funded by US National Institutes of Health grants4.
What the label dose means
Every oral trial here used BioResponse DIM, a formulated product designed to improve absorption124. In a 7-person US pharmacokinetic study, each 150 mg BioResponse DIM capsule contained 45.3 mg of DIM itself, so a trial's milligram figure may not match the DIM content of a plain powder capsule5. That study, funded by US National Institutes of Health grants, also found that the body converts DIM into several active breakdown products, which the authors said raises the possibility of interactions with drugs5.
The DIM page grades each trial. For other herbs sold for hormone-related symptoms, see our explainers on vitex for PMS, black cohosh for hot flashes and spearmint tea for PCOS.
Who should be careful
Check with a doctor or pharmacist before taking DIM if any of these apply:
- Taking tamoxifen: DIM lowered active tamoxifen levels, including endoxifen, in a 12-month trial, and the clinical effect is unknown1. Do not add DIM without the oncologist's input.
- A history of hormone-sensitive cancer or other hormone treatment: DIM changes estrogen metabolism and SHBG1, and its interactions with other hormone drugs have not been tested in the trials described here.
- Regular prescription medicines: the body breaks DIM down into several active compounds, and the researchers who found this flagged possible supplement-drug interactions5.
- Migraine: the UK trial's authors noted anecdotal reports that DIM may worsen migraine; headaches were reported by 18% on DIM and 12% on placebo, a difference that was not statistically significant2.
- Pregnancy or breastfeeding: the trials described here give no safety data for these groups12.
- Darker urine: reported by 31% of women on DIM versus 10% on placebo, which the trial authors described as a harmless by-product2.
Quick answers
Common questions
4 answersDoes DIM help hormonal acne?
Does DIM lower estrogen?
In the tamoxifen trial it shifted how estrogen was broken down and raised SHBG1; that is a change in markers, not a proven drop in estrogen effects or symptoms.
How much DIM was used in the trials?
Why does DIM change urine color?
Darker urine was the most common side effect in the largest trial, which the authors attributed to coloured DIM by-products2.
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Where to buy DIM (diindolylmethane)
Products from brands we partner with that contain DIM (diindolylmethane). Check the amount per serving against the doses studied, and the label for other ingredients.
DIM (diindolylmethane) products from partner brands
2 products Paid links · we earn a commission- Quick pickSupersmartDIM (Diindolylmethane)5% off with the Supersmart newsletterGet 5% off with the newsletter (paid link, opens in new tab)
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4 capsules: 400 mg plain DIM; 30 servings. Trials used the BR-DIM formulation at 150–300 mg/day; plain DIM at 400 mg has not been tested in them.
$25.00one-time$21.25subscribeChecked Oct 11, 2026 - HerbsProNOW Foods DIM 200 Diindolylmethane, 90 Veg Caps
1 veg capsule: 200 mg DIM (3,3′-diindolylmethane) with 100 mg calcium D-glucarate and 20 mg chlorophyllin
$16.74one-timeChecked Oct 14, 2026
References
5 sources. Numbers in the text link here.
Sources cited in this article
5 sources- 1A randomized, placebo-controlled trial of diindolylmethane for breast cancer biomarker modulation in patients taking tamoxifenBreast Cancer Res Treat, 2017 · PMID 28560655
- 2Effect of diindolylmethane supplementation on low-grade cervical cytological abnormalities: double-blind, randomised, controlled trialBr J Cancer, 2012 · PMID 22075942
- 3Oral diindolylmethane (DIM): pilot evaluation of a nonsurgical treatment for cervical dysplasiaGynecol Oncol, 2010 · PMID 19939441
- 4Phase Ib placebo-controlled, tissue biomarker trial of diindolylmethane (BR-DIMNG) in patients with prostate cancer who are undergoing prostatectomyEur J Cancer Prev, 2016 · PMID 26313229
- 53,3'-Diindolylmethane Exhibits Significant Metabolism after Oral Dosing in HumansDrug Metab Dispos, 2021 · PMID 34035125
DIM (diindolylmethane) and other dietary supplements are not intended to diagnose, treat, cure or prevent any disease, and these statements have not been evaluated by the FDA. Talk to your clinician or pharmacist before starting a supplement, especially if you take prescription medicines. Product links on this page are paid partner links.